Corrosion inhibitors



United States Patent Office 3,415,754

Patented Dec. 10, 1968 chemical reactions where contaminants are to be avoided 3,415,754 as much as possible.

CORROSION IlflHIBI'IZORS Chromium-nickel stainless steels have many admirable Ludo Midland; esslgllol to e Dow qualities, but they are susceptible to corrosion by hot Chemical Company, Midland, M1ch., a corporation of aqueous Sulfuric acid gg gf g Filed Feb. 28 1966 Ser. No. 530 407 5 I have found that if vanadyl sulfate or uranyl sulfate 8 Claims or a mixture thereof is added to aqueous sulfuric acid in a molar ratio of from about 0.25 to about 30 moles of the salt per mole of H 80 or acid salt of the sulfuric ABSTRACT OF THE DISCLOSURE acid, the corrosion rate of stainless steel is reduced, 10 markedly, even at temperatures as high as 170 C. for

The corrosive attack upon stainless steel by an aqueous extended periods of time. sulfate solutlon contammg H blsulfate or a An advantage of this invention is that it is possible to ture thereof, at a concentration level in the range of 0.3

to 3 normal is mark ed y reduced p adding to the solu employ stainless steel as a material of construction for react'on s stems u in f tron from about 0.25 to 30 moles of vanadyl sulfate or l y S g aqueous Sul unc acld or blsulfates as an ingredient. zg film?? g fi? there? f a H2504 The examples which follow are intended to illustrate i or lsu f m gfi 18 mar i g g at but not to limit the invention. In all instances, parts and igz g gfi gs as 1g as an over ex an 6 percentages are by weight unless otherwise specifically indicated. 20 Example 1 This invention relates to compositions and methods for A Solution of 3 molar V0504 in ()9 molar aqueous inhibiting the corrosion of stainless steels, and more par- Nell-I504 Was added to a Series of glass tubes- Test Samples ticularly pertains to compositions and methods for prolong, e and thick of S ai ess steels were tecting nickel and chromium-containing stainless steels p p one Sample of lhe metal under t st i u against the corrosive effects of hot sulfuric acid and acid merged in the test Solution and another Sample Of the salts thereof by adding vanadyl or uranyl sulfate or a same metal was suspended above the solution to check the mixture of th tw t aqueous 1f i id or an id corrosive effects of the vapors. A reflux condenser was alt of th id. connected to each tube and the solution in the tube was There are many he i l processes hi h require hi h heated to its boiling temperature. Each sample was tested concentrations of hydrogen ions where aqueous sulfuric 30 y under TefluX conditions at etmosphefie P acid or acid bisulfates are very effective as a catalyst. Sure- Among the reactions in which sulfuric acid is useful are The compositions of the metals and their orro ion hydrolysis, esterification, certain condensations and hys se t s are lat d low.

TABLE I Composition Corrosion rate (In./Month 10- Mo Ni Cr Mn 011 S1 Nb, Ta. Fe Liquid Vapor illlilfi 3 24 20 1 3.5 .125 .062 2 29 20 4 1 .029 .033 a 29 20 .75 3 1 .6 .075 .022

dration of olefins. These reactions are accelerated con- Example 2 siderably by heat. However, hot sulfuric acid is extremely u c r siv t m t m t l Th t l hi h are corro- A series of corrosion tests on three different stalnless sion-resistant to hot aqueous sulfuric acid and bisulfates Steel COIIIPOSIUOIIS was conducted in Sealed glass ampules are very expensive, so that they are used only to a very e temperatures of fef f y t0 y limited extent in reactors. Among such metals are tan- In an aq u 2 4 801110011 eentalhlhg t- The talu nd old, results of these tests are tabulated below in Table II.

The non-metals which can be used as construction ma- TABLE II terials for use with hot sulfuric acid or bisulfates are A glass, glass-lined or impervious carbon-lined reactors or $25 3 3 3" Ngfigity vosoghlgolar Common Rate P P In./Mon. 10

The shortcomings of glass and glass-lined chemical 140 .33 2.44 .08 equipment include brittleness, such that damage or breakg8 -5 32 .3g age can readily occur through relatively slight mechanical 140 44 shock, the low resistance to heat shock which can also 140 2.44 .141 develop cracks, and the low coeflicient of expansion as compared to metals, which results in strains in the glass Nelle of h eol'l'esloll rates are $0 h he to preclude on repeated cycles of heating and cooling. These h re the construction of reactors for use with the aqueous test comings require rigid inspection and maintenance consehltlefls the temPel'atllfes lhdleatedtrols on such equipment.

Impervious carbon lining is not completely satisfactory, Example 3 because hot sulfuric acid has a deleterious efiect on the To an ampule containing 20 rnl. of 3 N H 50 and 6 organic binder and on the carbon itself, which can be g. VOSO -2H O was added a piece of 316 stainless tubing gradually oxidized to volatile carbon oxides. In the procwith an CD. of inch, ID. of /6 inch, and weighing ess of oxidation, the surfaces which come into contact 1.0890 g. The ampule was heated for 9 days at C. with the hot sulfuric acid become pitted and difiicult to After the test, the tubing weighed 1.0009 g. This is equivmaintain in a state of cleanliness that is needed for many alent to a corrosion rate of 2.8 10 in. per month.

Example 4 The tests of this example were carried out in sealed ampules at 155-165 C. for 22 days, excepting one day when the temperature was lowered to 130 C. In each case, the .ampule contained 20 ml. of 3 N H 50 to which was added a uranyl or vanadyl sulfate in the amounts indicated below. The samples were 316 stainless tubing of the type defined in Example 3. Tabulated below are the solutions used and results obtained.

TAB LE III 2. The aqueous acidic solution as in claim 1 in which the compound is H 504 and the inhibitor is vanadyl sulfate.

3. In a method in which an aqueous solution from the class consisting of a solution of H 80 a solution of a bisulfate and a solution of a mixture thereof is used in contact with a stainless steel surface, the concentration of said solution being in the range of from 0.3 to 3 normal, the improvement which consists in:

modifying said aqueous solution so that it contains a small but corrosion inhibiting amount of at least one inhibitor selected from the group consisting of uranyl sulfate, vanadyl sulfate and mixtures thereof.

4. The method as in claim 3 in which the amount of inhibitor ranges from about 0.25 to about 30 moles per .mole of H 80 or bisulfate.

5. The method as in claim 3 in which the solution is a solution of H 80 6. The method as in claim 3 in which the stainless steel contains from about 18 to 20 percent by weight nickel,

Test Solution Corrosion Rate These data show that the addition of copper sulfate to the solution did not affect the protective action of vanadyl sulfate materially.

Although the examples show the use of the uranyl and vanadyl sulfates individually as corrosion inhibitors, they are also effective for this purpose in mixtures in any proportion up to their respective saturation concentrations in the aqueous sulfuric acid or bisulfate salt.

I claim:

1. An aqueous acidic solution, substantially non-corrosive to stainless steel and in contact therewith, consisting essentially of water and a compound selected from the group consisting of H 80 a bisulfate or mixtures thereof and at least one inhibitor of the class consisting of uranyl sulfate, vanadyl sulfate and mixtures thereof, the concentration of said H 80 bisulfate or mixture thereof being from 0.3 to 3 normal and the amount of inhibitor being from about 0.25 to about 30 moles per mole of said compound.

References Cited UNITED STATES PATENTS 2,513,131 6 /1950 Baer 252l47 XR 3,280,038 10/1966 Morris 252-101 XR 3,316,179 4/1967 Hoornstra et a1. 25279.2 XR

MAYER WEINBLATT, Primary Examiner.

US. Cl. X.R. 

